1. Field of the Invention
This invention pertains generally to multicast transmission, and more particularly to a protocol to coordinate multipoint groupwork in the IP-multicast framework.
2. Description of the Background Art
Internet computing is gradually migrating from the standard unicast transmission model to multicasting. In the IP multicasting model, a source needs to send a packet only once to the network interface, and multicast routers replicate the packet on its transmission path to multiple receivers. The Internet Group Management Protocol (IGMF) allows a host to join a multicast group by informing its local router to forward multicast traffic for this group to the leaf subnetwork where the host resides. Protocols such as DVMRF, MOSFF, and PIM perform the construction of multicast delivery trees and enable packet forwarding between routers.
With IP multicast, no guarantees are given for reliable or order-preserving delivery of packets, and a message is delivered on a best effort basis to all members of a multicast group. These shortcomings have spurred much research on reliable multicast between end hosts, and on mechanisms to refine IP multicast, such as using addressing information to enable subcasting or anycasting. Subcasting delivers or retrieves data between a source and select members of a multicast group, and anycasting transfers data to anyone member of a group, for example the nearest proxy from a group of servers. While IGMP targets group membership, and multicasting routing protocols are concerned with delivery, no protocols exist to tackle an emerging problem of multisite communication, which is group coordination. This problem surfaces especially for tightly coupled sessions featuring explicit conference membership control.
Group coordination denotes services to support distributed hosts in coordinating their joint activities, including synchronization of flows from different sources, ordered delivery of distributed event information, and the concurrent use of and access to shared resources, referred to as floor control.
Early paradigms of group coordination, mutual exclusion, or concurrency control, have been restricted to discrete data domains rather than multimedia contents, using locking to manifest control, and have not been deployed on an Internet scope. Online group coordination in relation to face-to-face meetings has been studied, and those studies show that greediness for time and bandwidth on behalf of non-cooperative users, as well as lack of social cues such as eye contact contribute to coordination problems. While geared toward supporting humans in their interactions, the concept of group coordination also applies to agent-based interaction. For example, methods to mediate resource contention at the user interface level are known. However, many existing systems for online collaboration are proprietary, sparsely documented, and limited to local area networks, or sessions with few users. These include token-based control mechanisms for a shared workspace, as well as systems in which distributed, task-activated floor control serves as a high-level analogy to collision-sensing in channel access.
Various other techniques have been developed as well, such as packet-switched voice conferencing in a broadcast and unicast setting, ITU standards 120 and 320 for video conferencing that are circuit-switched and designed for conferences with few users, the MCP coordination protocol between concurrent media flows based on token passing, frameworks for hierarchical collaboration looking at bandwidth and delay issues, mutual exclusion algorithms operating on a static logical propagation tree in which nodes maintain a pointer to the neighbor node that leads to the current token holder with access to the critical section, adding a dynamic link between a requester and the token holder to avoid backtracked routing of reply messages between a source and target node.
Notwithstanding the foregoing, there is a need to address how routing and end-to-end geometry used for multicasting data can also be used effectively for coordinating the activities among individuals and in sessions of Internet scope. The present invention satisfies that need, as well as others, and overcomes deficiencies in existing group coordination protocols.